Although glass plates used for display devices, picture frames, craftwork, containers, or the like are advantageous in that they have a small coefficient of thermal expansion, superior gas barrier properties, high transparency, good surface flatness, excellent heat resistance and chemical resistance, they tend to break easily and be heavy because of their high density.
Recently, as liquid crystal displays, organic light emitting devices, and electronic paper are arousing a growing interest, research on replacing the glass substrates used in such devices with plastic counterparts is gaining momentum.
A basic substrate, plastic film and a plastic substrate having a functional coating layer are advantageous over the glass plate in terms of light weight, ease of design, and impact-resistance. Also, an economic advantage may be attained from continuous manufacturing, compared to the glass substrate.
For a plastic substrate to be used in a display device, it should have a glass transition temperature high enough to endure the transistor processing temperature and the transparent electrode deposition temperature, oxygen and water vapor barrier properties so as to prevent aging of liquid crystals and organic light emitting materials, a small coefficient of thermal expansion and good dimensional stability so as to prevent deformation of the plate due to change of the processing temperature, mechanical strength comparable to that of the conventional glass plate, chemical resistance sufficient for enduring the etching process, high transparency, low birefringence, good surface scratch resistance, etc.
Among such properties, a low coefficient of thermal expansion (CTE) is a particularly important property, and a method of manufacturing a plastic film using a glass cloth is one of methods that provide a substrate having a low coefficient of thermal expansion.
To embody a low coefficient of thermal expansion (CTE), a tightly woven glass cloth should be used. As a glass cloth has a higher weaving density, the prepared plastic film has a lower coefficient of thermal expansion (see FIG. 4).
However, in the case where a film is manufactured by using the glass cloth along with organic materials such as epoxy and polymer, there is a limit in using a tightly woven glass cloth due to air bubble generated between glass fibers, and cracks may be generated at the interface due to a low interface adhesion strength between the glass cloth and organic materials.
A method of manufacturing films using organic materials and glass cloth is exemplified by US 2005/0203239, which discloses a method of dipping and curing a glass cloth in organic materials such as epoxy and polymers.
In this method, the surface of glass cloth is modified to improve the adhesion strength at the interface between the glass cloth and organic materials. However, there is a problem in that cracks are still generated at the interface due to the low interface adhesion strength.
In addition, when a film is manufactured by dipping the glass cloth in organic materials such as epoxy and polymers, a longer processing time for curing or solvent evaporation is required, so as to reduce its productivity.
Further, when a film is manufactured by dipping the glass cloth in organic materials such as the known epoxy and polymers, it is difficult to remove air bubble generated between the glass cloths due to high viscosity. In addition, to improve the problem, the process may be performed at a high temperature or under vacuum conditions, but the process becomes complex. Thus, the process cannot be easily performed.
Furthermore, when a film is manufactured by dipping the glass cloth in organic materials such as the known epoxy and polymers, a lamination process is employed. However, there is a problem in that it is difficult to perform a continuous process by the process.
Moreover, since the glass cloth has a wavelength-dependent refractive index that is different from that of the organic materials such as the known epoxy and polymers, it is difficult to manufacture a transparent film.